Silicone elastomer particles having a rubber elasticity have been used as a stress relaxation agent for resins. For example, heat-curable resins such as an epoxy resin are used to package electronic and electric parts. In such case, silicone elastomer particles are added to the resin so as to prevent the package from being broken easily even when a stress has been applied thereto due to the expansion of the resin as the electric parts generate heat. However, the problems are that silicone elastomer particles have a high cohesiveness as well as a low dispersibility in a resin, which makes it impossible for these silicone elastomer particles to sufficiently endow the resin with a stress relaxation effect; and that the strength of the resin may be impaired due to the agglomerated silicone elastomer particles.
In order to solve the above problems, the inventor of the present invention have proposed a type of silicone particles as silicone rubber spherical fine particles coated with a polyorganosilsesquioxane resin (Patent document 1). This type of silicone particles are characterized by having a rubber elasticity, a low cohesiveness, and a high dispersibility in a resin. Particularly, a type of silicone particles employing polymethylsilsesquioxane as a polyorganosilsesquioxane exhibits the lowest cohesiveness and the highest dispersibility. Such a type of silicone particles are obtained by adding organotrialkoxysilane to an aqueous dispersion of silicone rubber spherical fine particles, and then hydrolyzing and condensing the organotrialkoxysilane under a given condition(s).
However, in a case where this type of silicone particles is added to a resin composing a product that requires a cutting step after molding e.g. a printed board as such product, there has been a problem that the silicone particles may fall off a cutting surface in the cutting step. Moreover, there has been a concern that failures may occur in a wiring step as a result of allowing the fallen silicone particles to adhere to the surface of the product.
Here, it is considered that the silicone particles will not fall off if an adhesiveness between a resin and the silicone particles is improved. Further, for this reason, it is considered that the surface of a polyorganosilsesquioxane may contain organic groups that are reactive with the resin. For example, if desiring to allow the polyorganosilsesquioxane to contain alkenyl groups, polyalkenylsilsesquioxane may simply be employed as a polyorganosilsesquioxane. However, there has been a problem that this type of silicone particles as silicone elastomer spherical particles coated with polyalkenylsilsesquioxane has a high cohesiveness and a low dispersibility in a resin.
As mentioned above, silicone particles coated with polymethylsilsesquioxane have a low cohesiveness and a high dispersibility. Thus, a lower cohesiveness and a higher dispersibility can be achieved, if employing polymethylalkenylsilsesquioxane by introducing a methylsilsesquioxane unit into polyalkenylsilsesquioxane. However, with the production method described in Patent document 1, it is not possible to produce polymethylalkenylsilsesquioxane having alkenyl groups on the surface thereof.